The present invention relates to a method and apparatus for producing a liquid mixture having a pre-determined concentration of a specified component. More particularly, the present invention relates to such a method and apparatus in which component streams are mixed together to form an intermediate mixture having a lower concentration of the specified component than that desired for the mixture and a stream containing the specified component is added to such intermediate mixture so that the resultant stream has a pre-determined concentration of the specified component. Even more particularly, the present invention relates to such a method and apparatus in which part of the two component mixture is recycled to increase the homogeneity of the product.
There are many industrial processes that utilize liquid mixtures in which the concentration of the components of the mixture is particularly critical for the successful performance of the process. For example, in the manufacture of semiconductors, it is necessary that between processing steps, the wafer being processed be cleaned with an aqueous ammonia water solution.
The problem with producing such a solution with repeatable accuracy is that often the components are retrieved from bulk sources in which the components are mixed with other agents. As a result, the concentration of the components does not remain constant. For instance, in forming the aqueous ammonia solution, the ammonia component is drawn from a bulk source in the form of ammoniated water. Over time, however, the ammonia concentration within the water decreases due to the vapor pressure of the ammonia.
As will be discussed the present invention provides a method and apparatus for producing a liquid mixture with a reliably consistent concentration of the desired component.